Long range image projector



I March 25, 1958 YH. ELlON ET AL 2,827,831

LONG RANGE IMAGE PROJECTOR Filed Aug. 50, 1955 2 Sheets-Sheet 1 INVENTORS HERBERT ELION WALTEF H. THALL. BY

ATTORNEY- March 25, 1958 H. ELllON ET-AL 3 7 LONG RANGE IMAGE PROJECTOR Filed Aug. 30, 1955 2 Sheets-Sheet 2 f 2 *T i IMAGE-\ 5 P i s P 3 S i f i z 1 i q s WI.)

INVENTORS HERBERT ELION WALTER H. THALL.

W ATTORNEY United States 2,s27,ss1

LONG RANGE IMAGE rnorncron Herbert Elion, Danbury, and Walter H. Thali, Fairfield, Conn.

Application August 30, 1955, Serial No. 531,487

6 Claims. (Cl. 88-24) This invention relates to the projection of images for observation at relatively great distances from the projector, such as distances of from 1,000 to 18,600 feet-and more particularly to devices for projecting images on clouds, atmosphere-suspended layers of dust, mist, smoke and the like, and on large objects such as buildings and mountainsides or other distant objects of suflicient size and reflectivity.

It is primarily within the contemplation of this invention to provide means for producing an intense beam, for such long-distance projection, of substantially homogeneous luminous intensity throughout the transverse cross-section thereof, and whereby the resultant image is clear-cut and relatively undistorted, with a degree of message resolution not possible with conventional projectors. And it is our objective to accomplish this purpose by means of a long focus projector of relatively small proportions and with a projection lens of relatively small diameter for such a device.

Attempts to accomplish the above-mentioned objectives with conventional projectors have heretofore been without success. In those devices Where the conventional condenser lens is eliminated and reliance placed upon a reflecting surface for projecting a beam, it has been found that there is a considerable loss of the light emitted by the energy radiating source resulting in an inelficient device. And in those devices Where a conventional condenser is employed, it is invariably of very large proportions, which is not only costly, but also requires the use of special means uniformly to cool the large lens areas adjacent the source of intense heat. Where frosted or opalescent glass is used to prevent the image of the light source from being projected, there is also considerable loss of light, not only because of the translucency of the transmitting medium, but also because the resultant diffusion extends through a range of 180, some of the rays being scattered to regions outside that of the condenser lens. To overcome this defect, devices have been employed to catch and reflect such scattered rays of diffused light-resulting in an expensive apparatus and one not practically suited for cloud projection.

Another expedient heretofore attempted, with unsatisfactory results, has been the use of a mask or cut-ofl member in front of the message stencil to encircle the beam, for the purpose of cutting ofl the image of the light sourcesuch a mask being placed at the conjugate focus of the beam, for most effective masking effects. The use of a mask must necessarily result in a loss of efiiciency; and furthermore, because of its placement, the system requires an extremely large diameter, long focus projector lenswhich, as aforesaid, is expensive, besides being space-consuming and entails technical difiiculties in its maintenance.

To overcome the aforesaid shortcomings attempts have been made to employ various lens systems of different degrees of complexity; but these have proven satisfactory only for short-range projection, being ineflicient in the 2,827,831 Patented Mar. 25, 1958 light-gathering requirements projection.

In most conventional projection systems the message stencil is placed at the conjugate focus of the beam; and since the heat is most intense at that region, the stencil is difficult to handle and is subject to the deteriorating efiects of the heat.

it is within the contemplation of our invention to provide a projection system having none of the disadvantages and shortcomings of the conventional projectors hereinabove referred to. Our system employs a novel combination and arrangement of optical and projection components, the preferred form thereof employing, in place of the conventional condenser lens all portions of which have the same focus, a condenser lens with a plurality of Zones-adjacent refracting facets-each zone being corrected for spherical aberration, whereby there is no fall-ofl in brightness at the peripheral margin of the image. The arrangement is such as to enable the use of this type of condenser lens with a low focal-length to diameter ratio, for effective light gathering power, without diifusion losses. The preferred, but not exclusive, embodiment of our novel system is also characterized by the positioning of the message stencil between the conjugate focus and the multi-zoned condenser 1ensthe stencil being relatively close to the condenser and at a region of the beam of greater cross-sectional area than that of the conjugate focus area. The arrangement is hence such that the stencil is at a locale of comparatively low-heat intensity, thereby eliminating the danger and inconvenience of overheating. Moreover, the projection lens-as well as the message stencilare relatively close to the light sourcethereby resulting in a highefliciency light system and a clear-cut message image, permitting the use of a smaller projection lens than can be employed with conventional devices, and obviating the use of masks, opalescent or other diflusing media for eliminating the light source image. The novel arrangement above referred to results from a relationship of components not to be found in known devices, with results that are of critical importance in cloud projection.

Other objects, features and advantages will appear from the drawings and the description hereinafter given.

Referring to the drawings,

Fig. 1 is a semi-schematic side elevation of a projector embodying our invention.

Fig. 2 is a top view of Fig. 1.

Fig. 3 is a diagrammatic representation showing a preferred relationship between the main components of our invention.

Fig. 4 is a view like Fig. 3 showing another relationship of the components.

Fig. 5 is a view like Fig. 3 showing still another relationship of the components.

Fig. 6 is a diagrammatic representation of another form of our invention with a concave mirror reflector in place of the projection lens of the device of Figs. 3, 4 and 5, this view also showing the relationship of the main components in accordance with our invention.

Fig. 7 is a front view of a form of message stencil adapted for our invention.

Fig. 8 is a front view of a preferred form of condenser lens adapted for our invention.

The aforesaid main components of our invention as illustrated in Figs. 1-5 are a light source generally designated 10, condenser means 11, image stencil 12 and projection element or lens 13. In the embodiment of Fig. 6, a concave reflecting mirror 14 is employed in place of the said projection element 13.

As illustrated in Figs. 1 and 2, the said main components are housed within a structure which can be for successful cloud pivotally moved to change its elevation, and which can also be rotated in a horizontal'plane so that it can be swung to the desired azimuth. While Figs. land 2 illustrateone structure of a device embodying our inscope and intent of this invention.

- In -the particular form illustrated, a generally. cylin- 'drical casing 15 is mounted upon laterally opposite transverse shafts 16, these being disposed the bearings 17 at'the-upper terminal portions of the arms 19 of the yoke 18. An arcu'ate gear segment 20 is mounted on casing 15 and is in engagement with gear means 21 on said yoke 18, whereby the geared means 20 and 21 willbe in coactive engagement, in known manner, when the casing 15 is operatively rotated along the horizontal axis extending'through the said bearings 17. The said yoke 18 ismounted on a horizontal plate 2.2, the latter beingoperativelydisposed between th upper-and lower ball-bearing races 23'and 24 -the base plate 22 and said bearings being disposed'withinthe retainer or housing 25.

The threaded friction stop member 26, extending through flange 27 ,of said housing 25, is adapted ,to frictionally hold said'base plate 22 against movement. By this, ar-

' rangement, the entire yoke 18, together with the casing v15 supported thereby, can be horizontally rotated to swing the projector to the desired azimuth.

At the rear portion of the casing 15 is the housing 28 proportioned to contain therein the light source 10 (not'shown in Figs. 1 and 2), the door 29 permitting access to the interior of said housing. Disposed forwardly of said housing 28 is a special type of condenser 11, to be hereinafter specifically referred to, said condenser being contained WithiH a support 30. Disposed forwardly of said condenser 11 is said message stencil '12, the position of which can be predetermined by the operator, depending upon particular requirements. At the forward :portion of housing 15 is said projection lens 13, this being mounted within a frame 31 which carries upper and lowerslides 32 and 33. The upper slide 32 is in atslidable engagement, in known manner, with the upper guide rail 34. The lower slide 33 has afiixed theretothe internallythreaded collar 35 mounted over a the longitudinally disposed screw 36. The latter is opera'tively supported by the housing 37, the rearrnost portion of thescrew having afiixed thereto the crank handle 38. The arrangement is hence such that, upon amanipulation of crankhandle 38, the screw. 36 will revolve and operatively. move the projection lens 13 forwardly or rearwardly, as the circumstances require.

' Disposed in front of casing 15 is the mirror member 39 obtain suflicient light energy within a small space, for

'eife ctivecloud message projection. It has been found that the most favorable type of light source is a cooled, enclosed, high intensity metal vapor discharge lamp, or a combination of such lamps, thereby providing clean, heat-filtered illumination, eliminating vapor gases and such undesirable deposits which commonly result from open arcs and tail flames. The reference numeral, 43

7 identifies such source of illuminationthe reflector 44 ad acent thelight source being used in combination therewith for directing the beam of light through said condenser 11. For the purpose of this invention and the limiting relationships embodied therein, as hereinafter set forth, the brilliance of the light source should be greater'than 20,000 candles per square centimeter.

The condenser 11 is of the echelon type, comprising a plurality of lenticular zones f4 5each of said zones presenting a refracting facet corrected for spherical aberration. The multi-zone construction may vary in accordance with particular requirements-it being feasible, depending upon the circumstances, to employ concentric portions constituting the 'lenticular zones (like that of Fig. 8), or adjacent parallel zonal portions-the preferred arrangement being to have the stepped lenticular regions 45 disposed away from the light source. type of condenser, while used in certain types of searchlights, has never been used in combination with other components in a device for projecting sharp and clearcut images on clouds. This form of condenser, when used in combination with the other components 'of our invention, is adapted to attain our said objectives; and when so used, it transmits light without spherical aberrationnormally difficult or impossible to attain with ordinary lenses two feet in diameter-enables the .collection of relatively large quantities of light in a relatively uniform beam, andgives the required scattering or diffusion of light so as to eliminate the'projection of the image of the light source without using masks or, other complex mechanisms. V

The message stencil 12 is of generally conventional structure as shown in Fig. 7.1 It contains a plate '46 containing a perforated message portion 47 adapted topermit the passage. therethrough of light from the condenser We have discovered that there are certain relationships between the main components above-described which enable our various objectives to be attained-and which have not heretofore been obtainable with other devices employing different relationships. In order to define such relationships, the following system of notations will be employed in this specification:

f =focal length of condenser system, in the present case of condenser 11 d =diameter of condenser 11 f ==focal length of projection lens 13-or the concave projection mirror 14 d =diameter of projection lens 13 or projection mirror 14 c=length of the conjugate focus of the system comprising the reflector 44, light source 43 and condenserll s=distance between condenser 11 and message stencil 12 p=distance between message stencil 12 and the projection lens 13 or concave mirror 14 q=distance between projection lens 13 or projector mirror 14 and the image projected by said lens or mirror 7 The relationships we have discovered 'to render a device of this class operable for cloud projection are parable'to transmit a clear-cut message through the message,

stencil 12. Moreover, the heat at the region close to condenser 11 is much less than that at the C. F., so that undesirable heating of the stencil is eliminated.

We have also ascertained that for most effective operation of the'apparatus, the following relationship must prevail, where c. and s are of the proportions above indicated:

S22c-that is, the distance between the message stencil 12 and the condenser 11 is equal to or less than twice the conjugate focal distance c a Where s is greater than 20, the light available has been reduced to a point where'it is not practical for cloud pro-,

jection, requiring extremely large projection lens diam- This elefs. We have also found that, in addition to the above b'a'sic relationship, the distance ,p between the projec- 'Iion lens 13 (or mirror 14) and the message stencil 12, should be greater than three times the conjugate focal distance c-particularly with a long focal length projection lens or an extremely fast projection mirror (with 1 value less than 1). Otherwise, compound projection lenses or their equivalent must be employed, with the danger of accumulated aberrations and light losses. We have therefore found that the value p 3c is a necessary relationship, and makes possible the use of a simple lens or mirror system, in conjunction with a relatively fast condenser lens.

Using t. e iriultizcnal type of condenser, like condenser 11, we have found that such condenser operates efficiently and gives a uniform beam as long as the image distance q between the projector lens and the projected image is greater than 100 times the distance p between the projection lens 13 (or mirror 14) and the message stencil 12. In other words, another important relation is q lp.

As above indicated, the condensing means must be fastsufficient for effective light collection. The value f /a' must therefore be less than 3and preferably less than lfor efficient and satisfactory results.

In addition to the above relationships, the standard projection equation applies both for the arrangement according to Figs. 35, and Fig. 6, this equation being With further reference to the device according to Figs. 3, 4 and 5, I have ascertained that effective cloud projection can be obtained not only with the message stencil 12 disposed between the conjugate focus C. F. and the condenser 11, as shown in Fig. 3, out also when the message stencil is disposed forwardly of the conjugate focus as shown at Fig. 4, and at the C. F. as shown in Fig. 5.

The following are specific examples showing these relationships between the main components for the arrange ments of Figs. 36 inclusive-where c is 24 or less and sis 48" or less:

For Fig. 3, where the projection lens diameter (d is 24 and the focal length f of the projection lens is 72", f equals 24", equals 2 /2", c equals 24", q equals 5,000 and d equals 24.

For Fig. 4, where the projection lens diameter (01 is 24" and the focal length i of the projection lens is 72", f equals 24", .3 equals 43", 0 equals 24", q equals 5,000 and d equals 24".

For Fig. 5, where the projection lens diameter (d is 24 and the focal length f of the projection lens is 72", f equals 24", s equals 24", 0 equals 24", q equals 5,000 and d equals 24".

For Fig. 6, where the diameter (ri of concave mirror 14 is 60", f equais 2%", s equals 2", 0 equals 2", q

equals 1000 to 18090 and d equals 3".

In each of the four examples hereinabove given, the relationship limitations between the main components of the system as defined by the formulae hereinabove given are maintained. In practice they have enabled the projection of images over distances and with a degree of clarity never heretofore obtained with conventional devices.

In the above description, the invention has been disclosed merely by way of example and in preferred manner; but obviously many variations and modification may be made therein. It is to be understood, therefore, that the invention is not limited to any specific form or manner of practicing same, except insofar as such limitations are specified in the appended claims.

We claim:

1. In an optical system for the long range projection of images, a high intensity light source, a Fresnel type condenser lens having a low focal length to diameter ratio which is postioned adjacent said light source and which 6 transmits a beam of light from said source to a conjugate focus, a message-bearing stencil disposed forwardly of said Fresnel type lens at a distance no greater than twice said conjugate focus, a projection lens element disposed forwardly of said message-bearing stencil at a distance greater than three times the distance of said conjugate focus, a support for said Fresnel type lens, message-bearing stencil and projection lens element which holds said Fresnel type lens axially in a plane substantially parallel to the plane of the message-bearing stencil, said Fresnel type lens being operatively positioned closer to said message-bearing stencil than to said light source and thereby uniformly illuminating said message-bearing stencil at a location of lower heat intensity in the light beam from said source than exists at locations rearwardly of said Fresnel type condenser lens.

2. An optical system as recited in claim 1 in which said high intensity light source is positioned rearwardly of said Fresnel type lens, said light source being at a distance from the said Fresnel type lens equal to the conjugate focal length thereof and a concave reflector is positioned to the rear of said light source to direct a beam of light from said light source through said Fresnel type lens.

3. An optical system as recited in claim 1 in which said projection lens element includes a reflecting mirror.

4. An optical system as recited in claim 1 in which said message-bearing stencil is positioned between said Fresnel type lens and said conjugate focus.

5. In an optical system for the long range projection of images, a high intensity light source, a Fresnel type condenser lens having a low focal length to diameter ratio which is positioned adjacent said light source and which transmits a beam of light from said source to a conjugate focus, a message-bearing stencil disposed forwardly of said Fresnel type lens at a distance not greater than twice said conjugate focus, a projection lens element disposed forwardly of said message-bearing stencil at a distance greater than three times the distance of said conjugate focus, a support for said Fresnel type lens, message-bearing stencil and projection lens element which holds said Fresnel type lens axially in a plane substantially parallel to the plane of the message bearing stencil, said messagebearing stencil being positioned between said conjugate focus and said projection lens element, whereby said message-bearing stencil is illuminated at a location of lower heat intensity in the light beam from said source than exists at locations rearwardly of said Fresnel type condenser lens.

6. In an optical system for the long range projection of images, a high intensity light source, a Fresnel type condenser lens having a low focal length to diameter ratio which is positioned adjacent said light source and which transmits a beam of light from said source to a conjugate focus, a message-bearing stencil disposed forwardly of said Fresnel type lens at a distance no greater than twice said conjugate focus, a projection lens element disposed forwardly of said message-bearing stencil at a distance greater than three times the distance of said conjugate focus, a support for said Fresnel type lens, message-bearing stencil and projection lens element which holds said Fresnel type lens axially in a plane substantially parallel to the plane of the message-bearing stencil, said messagebearing stencil being positioned at said conjugate focus, whereby said message-bearing stencil is illuminated at a location of lower heat intensity in the light beam from said source than exists at locations rearwardly of said Fresnel type condenser lens.

References Cited in the file of this patent UNITED STATES PATENTS 1,333,303 Gage Mar. 9, 1920 (Other references on foilowing page) 1; 1: UNITED STATES PATENTS t 1;7ss,142

Granz Dec. 6, 1921 Halvorson Dec. 15, 1925 Bee chlyn -gNov. 29, 1927 Aldr Aug. 28, 1928 Bassett Jan.-6, 1931 

